The findings, published in the Archives of Internal Medicine, add to mounting evidence that Americans are overexposed to radiation from diagnostic tests, especially from a specialized kind of X-ray called a computed tomography, or CT, scan.

“What we learned is there is a significant amount of radiation with these CT scans, more than what we thought, and there is a significant number of cancers,” said Dr. Rita Redberg, editor of the Archives of Internal Medicine.

“It’s estimated that just from the CT scans done in one year, just in 2007, there will be 15,000 excess deaths,” Redberg said.

“We’re doing millions of CT scans every year and the numbers are increasing. That is a lot of excess deaths.”

CT scans give doctors a view inside the body and involve much higher radiation dose than conventional X-rays. A chest CT scan exposes the patient to more than 100 times the radiation dose of a chest X-ray.

About 70 million CT scans were done on Americans in 2007, up from 3 million in 1980.

“While certainly some of the scans are incredibly important and life saving, it is also certain that some of them were not necessary,” Redberg said.